This invention relates to a process for preparing polyurethane-backed textiles.
Polyurethane backings are being increasingly used in preparing carpet and other textiles. The polyurethane backing improves the textile by adding bulk and stiffness, by securing pile fibers to the primary backing of the textile, by increasing the dimensional stability of the textile, and the like. The use of such polyurethane backings is described, for example in U.S. Pat. No. 4,296,159 to Jenkines et al.
The composition of the polyurethane-forming formulation used to prepare the textile backing is determined by at least three competing factors. First, the backed textile must display minimal tendency to curl or otherwise become distorted over time. Second, the backing must be as tack-free as possible, so that the textile does not stick to itself or other materials during storage and use. Third, the backing must strongly adhere to the substrate textile.
It has been found that formulation modifications which improve dimensional stability tend to increase tack and decrease the adhesion of the backing to the textile. Thus, the development of polyurethane textile backings has been characterized by compromising improvement in one of these properties for improvement in another.
In addition to the problems in achieving optimal properties in the backed textile, application of the polyurethane to the textile has also proven difficult. In commercial textile backing operations, there is very little latitude in processing parameters. It has been found, that in these operations, small changes in any number of processing conditions could lead to inferior or unusable product. In particular, small changes in the isocyanate index (100 times the ratio of isocyanate equivalents to active hydrogen equivalents) could cause the production of inferior product. In addition, it has been found that conditions of humidity and moisture absorption by the fibers of the textile have substantial effect on the processing of the polyurethane composition, making the process even more difficult to control. Further, the reactivity of the composition must be carefully controlled to permit the composition to be formed into a layer and gauged to the proper coating weight, yet cure quickly thereafter.
Accordingly, it would be desirable to provide a textile having a polyurethane backing which exhibits excellent dimensional stability, strong bonding to the substrate and low residual tack. In addition, it would be desirable to provide a polyurethane forming composition which is more easily processed than polyurethane forming compositions which are conventionally employed to prepare textile backings and which provides the desired dimensional stability, tack and adhesion.